This invention relates to porous polymeric biosupports, particularly porous nylon biosupports. In one aspect, this invention relates to use of porous polymeric biosupports in processes for biodegradation of aqueous waste streams containing organic contaminants. In another aspect, this invention relates to use of porous polymeric biosupports in packed bed and fluidized bed reactors for biotreatment of aqueous waste streams. In a further aspect, this invention relates to the process for preparing the porous polymeric biosupports.
Commercial utilization of immobilized bacteria technology (IBT) for cost-effective biological treatment of chemical wastes has been increasing. IBT utilizes highly selected, chemical-degrading bacteria in bioreactors designed to provide optimal conditions for microbial activity.
In IBT, biosupports are hosts for the bacteria which degrade toxic or polluting chemicals in waste streams into environmentally harmless products. This is usually done by flowing the waste stream through a reactor vessel containing the bacteria on a biosupport media.
Chemical degrading bacteria immobilized in bioreactors have been shown to achieve exceptional performance for the biotreatment of chemical industry wastes. Use of IBT in fluidized bed reactors (FBRs) and packed bed reactors (PBRs) achieve high rates of chemical removal, tolerate harsh conditions, survive dormancy, tolerate surge loadings, and produce lower levels of biological solids than conventional waste treatment technologies.
The biosupports which are typically used in commercial scale bioreactors are predominantly sand, granular activated carbon (GAC) particles and porous inorganic particles such as diatomaceous earth, alumina oxide and sintered glass. Although these biosupports, also known as biocarriers, are commercially available and have been well-proven as supports for chemical-degrading bacteria, they all have some disadvantages. The GAC and inorganic biosupports are expensive and experience attrition of 5-20% per year. In addition, the removal of excess biomass from these biosupports is problematic since their high density and fragility make vigorous back-flushing or mechanical biomass separation difficult. Sand is affordable and non-fragile, but requires a significantly longer period of time for microbial colonization (slower startup) and lacks the advantage of chemical adsorption as a supplementary removal mechanism. In addition, microorganisms on sand are more prone to performance failure and slow recovery after physical or chemical upsets.
Lodaya et al (U.S. Pat. No. 5,403,487) has disclosed the use of microporous synthetic resinous materials, including nylon, as biosupports for use in treating aqueous waste streams in aerated packed bed reactors. The microporous synthetic resinous materials of Lodaya et al have a density less than the density of water, i.e. float in the reactor, and therefore require a screen to hold the resin particles in place. The density of the microporous synthetic resinous materials of Lodaya et al creates the significant problem of not being able to handle biofouling and biomass control in the packed bed reactor. The packed bed reactor of Lodaya et al also requires use of a recycle stream. In addition, the microporous synthetic resinous materials of Lodaya et al cannot be used in fluidized bed reactors because they float.
A biosupport material which solves the problems of the commercially available biosupports and of materials such as those disclosed in Lodaya et al would be highly desirable. It has now been found that the porous polymeric biosupports of the invention solve the above-described problems. Specifically, the porous polymeric biosupports of the invention have the following advantages: (1) high porosity permitting rapid and heavy colonization by inoculated bacteria, (2) large pore sizes and open structure promoting higher levels of microorganism growth inside the biosupport and resulting in greater tolerance to upsets, less biomass loss during fluidization and higher overall performance, (3) high physical strength eliminating attrition, (4) inert to most chemicals and waste streams, (5) density slightly greater than the density of water eliminating the problems of Lodaya et al and permitting simple, cost-effective fluidization by air injection to control biomass in PBRs, (6) high rigidity providing good abrasion of excess biomass during fluidization, (7) chemical biodegradation rates equal to or exceeding commercially available biosupports, and (8) production process allowing flexibility in size, density, porosity and composition of the biosupports.
The porous polymeric biosupports of the invention also have the advantage of utilizing waste polymer or recycle polymer as feedstock. This utilization of waste or recycle polymer is an environmentally friendly process resulting in waste recycling and reduction.